The main problem with these displays is that when exposed to too much hot sun, the LCD panel ‘bleeds’.   Over time, this makes it increasingly illegible, not to be mention ugly.    I previously fixed the displays in both my old 300SE and the 560SEC.    The W124 outside temperature display is basically the same as the unit found in the W126 and W124.  They are just in different housings.

The good news is that replacement LCD panels are available.    The LCDs used changed in about 1988, so for the 300TE I needed to use the newer version of the LCD panel.    I also bought another earlier one to fix a spare W126 unit I have on hand.

The W124 outside temperature display unit just screws into the back of the instrument cluster.   Its the first thing you have to remove to get the gauges out, so now was a good time to repair it.

To repair the W124 unit, there are four small screws that must be removed.   On this model, the upper and lower parts of the housing must come apart to get to the front part where the LCD panel is.

The later unit as on my 300TE has a more sophisticated baffle for the bulb that illuminates the display.   Otherwise there are basically the same, with the two black ‘blocks’ that transmit the signal from the PCB to the LCD panel.     The dot at the top of the LCD panel faces upwards.

As I purchased two LCD panels, a new one and an old one, I had the issue of not being able to work out which was which.   Probably it would be evident with a strong magnifying glass, but I couldn’t tell.   I tried one, and as it turned out, it was the wrong one.    The W124 outside temperature display is a separate unit to the instrument cluster, so its possible to test it without installing the entire instrument cluster.

It also looks like the blub in my unit has blown.  It would be easy to change if you are good at soldering.   This is soldered onto the PCB, and I’m terrible at soldering.   For now, I’m going to leave it as is.    I’m still pretty happy with this repair.

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I found a few things to speed up the process while doing the second car.   Firstly, the instrument cluster does not need to be unplugged.   It is possible to remove the 560SEC outside temperature display unit by just sliding the instrument cluster out of its housing, but not disconnecting any of the cables (other than the temperature one).    You just need a stubby Phillips head to get in behind the cluster and remove the two screws that hold in the temperature display unit.

The photo above shows the 560SEC outside temperature display unit removed from the car and dismantled.   Interestingly the 1987 unit used small Phillips head screws to hold the front of the display on. The 1986 unit had flat head screws.   Other than that, they seemed identical.     The SEC unit was stamped 5/87 which seems correct.   I forgot to look on the 300SE.  As per last time, that small dot in the border of the LCD unit indicates the top.   You can also see the little blocks that conduct the signal to the LCD panel are still on the old display.

The picture is showing the old LCD still in the display unit.   Behind the LCD unit there is a small piece of a paper like material that sits on the inside of the LCD.   I left that with the old LCD screen when doing the 300SE.  As the 300SE’s screen was so bright with the headlights on, I transferred it over on the SEC.   I would recommend transferring this paper.   It makes sure the brightness level is appropriate. I have saved the paper from the 300SE, so I can add it back in next time I have to remove the instrument cluster.

The picture above shows the repaired 560SEC outside temperature display, along with the two dead units.   It also shows the piece of paper that should go in the 300SE unit.     To make sure I did the repair properly, I did a quick test before pushing the instrument cluster back into the dash.   I was rewarded with a perfectly working outside temperature.

The way these units are so easy to fix also means it is an easy job to have your car in Celsius or Fahrenheit.   A used display with a cloudy LCD would be quick cheap, and then it could be fixed and put into the car.   I would have converted to Celsius when I lived in the USA.  I could never really get my head around imperial measurements.

Finally, I tested with the lights on and the illumination was a little dimmer than on the 300SE, thanks to that paper.  As it was all working perfectly, I pushed the cluster back in place.    Last step was to replace the drivers side speaker, and the job was done.

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The W126 Outside temperature LCD repair is really easy.   It should be on the radar of any W126 (or W124) owner who has a failing outside temperature display.   It only took 30 minutes and is very easy.   Even better, the LCD illumination works when the headlights are on, when I thought it was broken.    I guess the old LCD was so cloudy the light couldn’t get through.

This is my second attempt to fix the W126 Outside temperature LCD.   The first time, I bought the wrong LCD panel and them mounted it upside down.    After seeing the preliminary results, I was confident enough to order two more displays in Celsius to fix the 300SE and 560SEC.   Last time I wasn’t sure which way up the LCD went.   On closer inspection, there is a small dot in the centre on one of the long sides.   I was able to reverse how it had it previously.    Considering the ease replacement and the impact it has on the car, the new LCD panel is very good value.

The photo above shows the two new W126 outside temperature LCD panels and the broken old one.   As with my prior attempt, the little back contact blocks need to be re-used in the temperature display unit.   As long as you’re careful, it is very easy to mount the new LCD panel.     It was a nice day when I fitted the panel today, but I can remember the display on my old 560SEC in Michican reading -20F.

Now the fix is done for my 300SE, next is to remove the instrument cluster and also repair the 560SEC display.

Update – 27/4/21:  I have now completed the job on the 560SEC too.   See that article for more details, especially how to ensure the display is not too bright.

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Buying a used one is not really a good option.   They are not particularly cheap, and even if a cheaper one from the USA can be sourced, it would be in Fahrenheit.   There is somebody in Europe who is selling replacement LCD panels so I thought I would give it a go.

Obviously to get to the LCD, the instrument cluster has to come out.   I find the easiest way is to remove the drivers side speaker and push it out from the back.   The W126 outside temperature display is screwed into the bottom of the cluster and can be removed without any other disassembly.

Replacing the LCD is as simple as taking the front off and then swapping the panels over.

The little contacts on each side of the panel also need to come too.   When doing it, I couldn’t work out which side was the top.  I ended up guessing and I was wrong.   I guess I had 50/50 chance.

The backlight is also broken on my 300SE, so I dismantled the W126 outside temperature display to see if I could change it.   At first glance it looks like the little bulbs used in the dashboard.   However, its actually soldered to the circuit board.   My soldering skills are not up to this task so I don’t think I will replace it.

I got it back into the car and found two problems.   The first one is simple, I had the LCD upside down.   The second is more serious.   I didn’t read the description properly of the LCD, so didn’t specify I wanted Celsius.   The panel I have is for Fahrenheit which is useless to me.    So I guess that is about $65 down the drain, although I might be able to sell the panel.

I’ve now ordered two new panels to do the job properly and learn from my mistakes this time.

Despite my careless buying I feel good about this improvement.  The repair can be done without soldering, and seems to work quite well.   I should now have working temperature displays in these cars once the new LCD panels come in.

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